C++STL

1. vector

• Description: variable length array with multiplication idea

• Function:

  1. size(): returns the number of elements (almost all containers have)
  2. empty(): Returns whether it is empty (almost all containers have)
  3. clear(): clear
  4. front()/back(): returns the first / last element in the vector
  5. push_back()/pop_back(): insert an element after the vector / delete the last element of the vector
  6. begin()/end(): returns the position of the first element of the vector / returns the position after the last element of the vector

• Supplement: it can be accessed using [] like an array

• use:

  #include <iostream>
  #include <cstdio>
  #include <algorithm>
  #include <cstring>
  #include <vector>
  using namespace std;
  
  int main(void)
  {
  	vector<int> a(10, -1); // Define a vector with a length of 10 and assign each value to - 1
  	a.size(); // Container length, O(1) all containers have
  	a.empty(); // Whether the container is empty, O(1) all containers have
  	for (auto x : a) cout << x << endl;
  
  	vector<int> b;
  	for (int i = 1; i < 10; ++i) b.push_back(i);
  	for (int i = 0; i < b.size(); ++i) cout << b[i] << endl; // The first traversal method
  	for (vector<int>::iterator i = b.begin(); i != b.end(); ++i) cout << *i << endl; // The second traversal method
  	for (auto x : b) cout << x << endl; // The third traversal mode is a new traversal mode in C++11
  	return 0;
  }
  

2. pair entered by mistake

• Brief description: integrate two data into one data

• use:

  1. First: first element
  2. Second: the second element (comparison operation is supported, with first as the first keyword and second as the second keyword)

  #include <iostream>
  #include <cstdio>
  #include <algorithm>
  #include <cstring>
  #include <vector>
  using namespace std;
  
  int main(void)
  {
  	pair<int, string> p;
  	// There are two ways to create pair s
  	p = make_pair(1, "moyan");
  	p = { 1, "moyan" }; // C++11
  	cout << p.first << " " << p.second << endl;
  	return 0;
  }
  

3. string

• Description: String

• Function:

  1. size(): returns the length of the string
  2. empty(): Returns whether the string is empty
  3. clear(): clear string
  4. substr(): returns a substring. The first parameter is the starting position and the second parameter is the length (subscript starts from 0)
  5. c_str(): returns a C language style string, which is used for printf to output string type strings

• use:

  #include <iostream>
  #include <cstdio>
  #include <algorithm>
  #include <cstring>
  #include <vector>
  #include <string>
  using namespace std;
  
  int main(void)
  {
  	string a = "abc";
  	a += "def";
  
  	cout << a << endl;
  	cout << a.substr(1, 2) << endl;
  	printf("%s\n", a.c_str());
  	return 0;
  }
  

4. queue

• Brief description: queue, first in first out

• Function:

  1. size(): returns the number of elements (almost all containers have)
  2. empty(): Returns whether it is empty (almost all containers have)
  3. push(): inserts an element at the end of the queue
  4. front(): returns the queue header element
  5. back(): returns the end of queue element
  6. pop(): pop up the queue header element

• use:

  #include <iostream>
  #include <cstdio>
  #include <algorithm>
  #include <cstring>
  #include <vector>
  #include <queue>
  using namespace std;
  
  int main(void)
  {
  	queue<int> q;
  	q.push(1);
  	q.push(2);
  	q.push(3);
  	while (!q.empty())
  	{
  		int tmp = q.front();
  		q.pop();
  		cout << tmp << endl;
  	}
  	return 0;
  }
  

5. priority_queue

• Brief description: priority queue, also known as heap, defaults to large root heap.

• Function:

  1. size(): returns the number of elements (almost all containers have)
  2. empty(): Returns whether it is empty (almost all containers have)
  3. push(): insert an element
  4. top(): returns the heap top element
  5. pop(): pop the top of heap element

• use:

  #include <iostream>
  #include <cstdio>
  #include <algorithm>
  #include <cstring>
  #include <vector>
  #include <queue>
  using namespace std;
  
  int main(void)
  {
  	priority_queue<int> q; // Big root pile
  	q.push(1);
  	q.push(2);
  	q.push(3);
  	while (!q.empty())
  	{
  		int tmp = q.top();
  		q.pop();
  		cout << tmp << endl;
  	}
  	priority_queue<int, vector<int>, greater<int> >heap; // Small root pile, increasing from top to bottom
  	heap.push(1);
  	heap.push(2);
  	heap.push(3);
  	while (!heap.empty())
  	{
  		int tmp = heap.top();
  		heap.pop();
  		cout << tmp << endl;
  	}
  	return 0;
  }
  

6. stack

• Description: stack, first in first out, also known as last in first out

• Function:

  1. size(): returns the number of elements (almost all containers have)
  2. empty(): Returns whether it is empty (almost all containers have)
  3. push(): inserts an element into the top of the stack
  4. top(): returns the stack top element
  5. pop(): pop up stack top element

• use:

  #include <iostream>
  #include <cstdio>
  #include <algorithm>
  #include <cstring>
  #include <vector>
  #include <queue>
  #include <stack>
  using namespace std;
  
  int main(void)
  {
  	stack<int> s;
  	s.push(1);
  	s.push(2);
  	s.push(3);
  	while (!s.empty())
  	{
  		int tmp = s.top();
  		s.pop();
  		cout << tmp << endl;
  	}
  	return 0;
  }
  

7. deque

• Brief description: double ended queue, which can be called enhanced vector, is relatively slow, that is, the efficiency is low
• Function:
  1. size(): returns the number of elements (almost all containers have)
  2. empty(): Returns whether it is empty (almost all containers have)
  3. clear(): clear
  4. front()/back(): returns the first / last element in deque
  5. push_back()/pop_back(): insert the last element of deque / delete the last element of vector
  6. push_front()/pop_front(): insert an element to the front of deque / delete the front of deque
  7. begin()/end(): returns the position of the first element of the vector / returns the position after the last element of the vector
• Supplement: you can also use [] for random access

8. set，map，multiset，multimap

• Description: Based on balanced binary tree (red black tree), dynamic maintenance sequence

• Function:

  1. size(): returns the number of elements (almost all containers have)
  2. empty(): Returns whether it is empty (almost all containers have)
  3. clear(): clear
  4. begin()/end(): returns the iterator of the first element of the container / returns the iterator of the last element of the vector

  • set/multiset:

    1. insert(): inserts a number
    2. find(): find a number
    3. count(): returns the number of a number
    4. erase(): there is one parameter. If the parameter is a number x, delete all x in the container (time complexity O (K + logn), where k is the number of x). If parameter is an iterator, iterator is deleted
    5. lower_bound()/upper_bound(): the two core functions. lower_bound(x) returns the iterator that is greater than or equal to the minimum number of X, upper_bound(x) returns an iterator that is greater than or equal to the maximum number of X.

  • map/multimap:

    1. insert(): the number of inserts is a pair
    2. erase(): the input parameter is pair or iterator
    3. find()
    4. [] (time complexity is O(log n))
    5. lower_bound()/upper_bound()

    #include <iostream>
    #include <cstdio>
    #include <algorithm>
    #include <cstring>
    #include <vector>
    #include <queue>
    #include <stack>
    #include <map>
    using namespace std;
    
    int main(void)
    {
    	map<int, string> m;
    	m.insert({ 1, "Zhang San" });
    	m.insert({ 2, "Li Si" });
    	cout << (*m.find(1)).second << endl;
    	cout << m[1] << endl;
    	return 0;
    }
    

9. unordered_set, unordered_map,unordered_multiset,unordered_multimap

• It is similar to the above set, map... But the addition, deletion, modification and query time is O(1) and lower is not supported_ bound/upper_ bound
• Implementation based on hash table

10. bitset

• Description: pressure level
• Usage: BitSet < 10000 > s (10000 is digits)
• The following operations are supported:
  1. ~，&，|，^
  2. >>,<<
  3. ==,!=
  4. []
  5. count() returns the number of 1s
  6. any() determines whether there is at least one 1
  7. none() determines whether all are 0
  8. set() sets all positions to 1
  9. set(k, v) changes the k-th bit to v
  10. reset() changes all bits to 0
  11. flip() is equivalent to~
  12. flip() reverses the k-th bit